>>> Mark Wielaard <mjw@redhat.com> 02/21/12 11:08 PM >>>>On Tue, Feb 21, 2012 at 03:26:30PM +0000, Jan Beulich wrote:>> >>> On 21.02.12 at 15:43, Mark Wielaard <mjw@redhat.com> wrote:>> > For DW_CFA_def_register DWARF4 explicitly says so: "This operation is>> > valid only if the current CFA rule is defined to use a register and>> > offset." So one needs to use CFI_DEF_CFA with both a register and an>> > offset here after the def_cfa_expression.>> >> Hmm, that's in contrast to the gas implementation (but I'd certainly>> give the specification preference if it explicitly states so, so gas>> should at least emit a warning here rather than considering this>> valid).>>I am afraid gas cannot help us here. Since like you pointed out in your>patch:>>This requires the use of .cfi_escape (allowing arbitrary byte>streams to be emitted into .eh_frame), as there is no>.cfi_def_cfa_expression (which also cannot reasonably be>expected, as it would require a full expression parser).>>So we are on our own here.

Hmm, yes, probably it wouldn't be nice if gas reset all its state when.cfi_escape is used.

>> But provided the specification mandates this, I'm okay with the change>> in principle. Just that specifying an offset of 0 doesn't look right then.>>Yeah, I dunno what I was thinking. The offset should be set to the offset>that was there before when rsi was pushed. The attached patch does that>by using the same value as was used at the start of common_interrupt.>Does that look OK?

I would have thought that it should be SS+8-RBP (as %rbp is at the topof the stack at that point). I can't verify this immediately, though, as I'mnot in the office today.